1. Field of Invention
This disclosure relates in general to testing equipment on blowout preventer (BOP) systems for operability and wear. More specifically, this disclosure relates to testing the operation of valves in a BOP system subsea before, during, and after closed high-pressure BOP testing.
2. Related Technology
BOP systems are hydraulic systems used to prevent blowouts from subsea oil and gas wells. BOP equipment typically includes a set of two or more redundant control systems with separate hydraulic pathways to operate a specified BOP function. The redundant control systems are commonly referred to as blue and yellow control pods. In known systems, a communications and power cable sends information and electrical power to an actuator with a specific address. The actuator in turn moves a hydraulic valve, thereby opening fluid to a series of other valves/piping to control a portion of the BOP.
Many BOP systems are required to be safety integrity level (SIL) compliant. In addition, most modern BOP systems are expected to remain subsea for up to 12 months at a time. In order to decrease the probability of failure on demand, BOP control valves need to be tested while they are subsea without requiring extra opening and closing cycles of the BOP or requiring additional high pressure hydraulic cycles to close the bonnets solely for testing purposes. Various types of control systems can be safety rated against a family of different standards. These standards may be, for example, IEC61511 or IEC61508. Safety standards typically rate the effectiveness of a system by using a safety integrity level. The SIL level of a system defines how much improvement in the probability to perform on demand the system exhibits over a similar control system without the SIL rated functions. For example, a system rated as SIL 2 would improve the probability to perform on demand over a basic system by a factor of greater than or equal to 100 times and less than 1000 times.
One issue with attaining a safety integrity level rating for subsea hydraulic equipment is lack of ability to test each valve in the system and ascertain its functionality without retrieving the valve from the sea floor. BOP systems often utilize several valves working together to activate a function in a single circuit. While some have suggested placing diagnostics on each and every valve in a BOP system, such a solution is impractical and difficult to execute in practice.